Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 issued to Cruex discloses the basic construction of a scroll type fluid displacement apparatus. This apparatus includes two scrolls each having a circular end plate and a spiroidal or involute spiral element. The scrolls are maintained at an angular and radial offset so that both spiral elements interfit to form a plurality of line contacts between their curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets increases or decreases, dependent on the direction of the orbital motion. Thus, a scroll type fluid displacement apparatus may be used to compress, expand, or pump fluids.
Referring to FIG. 1, a conventional scroll type fluid compressor 1 includes a compressor housing 2 having a front end plate 3 mounted on a cup-shaped casing 4 by bolt 5. A fixed scroll 6 and an orbiting scroll 7 are placed in compressor housing 2. Fixed scroll 6 includes end plate 61, spiral element 62 which is formed on a front axial end surface of end plate 61, and projecting portion 63 which is formed on the opposing rear axial end surface of end plate 61. Projecting portion 63 includes dividing wall 631 and a plurality of shank portions 632. Projecting portion 63 is fixed on the inner wall surface of bottom portion 41 of cup-shaped casing 4 by bolts 8. Bottom portion 41 includes dividing wall 411 and shank portions 412. Bolts 8 are disposed through holes 412a in shank portions 412 and holes 632a in shank portions 632. End plate 61 of fixed scroll 6, which is secured to cup-shaped casing 4 as described above, divides the interior of cup-shaped casing 4 into rear chamber 42 and front chamber 43. Seal ring 9 seals between the outer surface of end plate 61 of fixed scroll 6 and the inner surface of cup-shaped casing 4.
Orbiting scroll 7 includes end plate 71, spiral element 72 which is formed on a front axial end surface of end plate 71, and tubular bore 73 which is formed on the opposing rear axial end surface of end plate 71. Spiral element 72 interfits with spiral element 62 of fixed scroll 6 at an angular and radial offset to form a plurality of line contacts to seal off fluid pockets in a manner known in the art. Orbiting scroll 7 is coupled to drive shaft 10 which is rotatably supported within front end plate 3 through radial bearing 31. The drive mechanism which drives orbiting scroll 7 without rotation is known in the art. Examples can be found in U.S. Pat. Nos. 4,439,118 and 4,547,138.
When orbiting scroll 7 undergoes orbital motion, the fluid, which flows into a suction chamber in front chamber 43 from suction port 11 formed on cup-shaped casing 4, is taken into the fluid pockets formed between spiral elements 62 and 72. The fluid is gradually compressed as it is moved toward the center of the spiral elements. Compressed fluid at the center of the spiral elements exits into a discharge chamber formed in rear chamber 42 through discharge hole 611 formed through end plate 61 of fixed scroll 6. The compressed fluid is discharged out of compressor housing 2 through discharge port 12 formed on cup-shaped casing 4.
In the above compressor, threaded hole 632a is formed in shank portion 632 of projecting portion 63 to receive bolt 8 to fasten cup-shaped casing 4 to fixed scroll 6. A certain axial length for hole 632a and shank portion 632 is required to adequately secure cup-shaped casing 4 to fixed scroll 6. This axial length for shank portion 632 is larger than the required dimension which is needed to define a suitable discharge chamber. Thus, the axial length of compressor 1 becomes longer solely to accommodate this connection.
In addition, seal ring 13 is disposed between the outer surface of cup-shaped casing 4 and bolt 8 to prevent leakage of discharged gas from rear chamber 42 to the outside. However, when the discharged gas pressure is high gas nonetheless leaks from rear chamber 42 to the outside through a small gap adjacent seal ring 13, although the volume of this gas leakage is small.
FIG. 2 shows the rear axial end surface of a fixed scroll of a conventional scroll type fluid compressor. Fixed scroll 6 is originally made by casting. The rear axial end surface of end plate 61 and the axial end surface of projecting portion 63 are planed by cutting or machining. However, since surrounding area 612 of projecting portion 63, including dividing wall 631 and shank portion 632, cannot be finished by cutting, an unfinished casting surface still remains on the surface of surrounding area 612. The surface of surrounding area 612 is lower than the surrounding finished portions of end plate 61.
If valve retainer 14 and valve plate 15 were fixed to surrounding area 612, discharge hole 611, which is disposed on a higher, finished portion of end plate 61, would not be securely closed. Therefore, valve retainer 14 which limits the opening volume of valve plate 15 cannot be fixed on the unfinished surface of surrounding area 612. Valve retainer 14 and valve plate 15 must be fixed to a finished portion of the surface of end plate 61 by bolt 16. Valve retainer 14 and valve plate 15 must be fixed to the portion of the finished surface outside of projecting portion 63 as shown in FIG. 2. If valve retainer 14 and valve plate 15 were attached inside of projecting portion 63, their lengths would be very short. This increases the angle through which valve retainer 14 and valve retainer 15 must bend to open discharge hole 611 and significantly reduces their durability. Thus, valve retainer 14 and valve plate 15 must be fixed to the outer edge of end plate 61.